Studies continued on effects of maternal immunization and chemical agents in the environment on the immune response to pneumococcal polysaccharides (PSs) conjugated to inactivated pneumolysin (ply). Various conjugation techniques including reductive amination and PS-derivatization were tried to improve the stability and immunogenicity of the PS antigen. Young mice from mothers, that were immunized with type 9V PS, inactivated pneumolysin (ply) or 9V PS-ply conjugate during gestation, received an additional dose of the same antigen after birth. The dose induced higher specific IgM antibody response compared to the same dose in non-treated controls. Studies were also conducted to examine the toxic effects caused by interactions of certain drugs and biological products with the immune system. Pregnant mice at 14 days of gestation were injected with cortisone acetate or Fenition, an organic phosphorus insecticide. After birth, young mice at 3 weeks of age were exposed in an inhalation chamber to the same chemicals. Later, the young mice were injected with type 9V PS-ply conjugate. At 5 weeks of age, serum samples were collected, and 9V IgG and 9V IgM antibody responses are being determined. These studies suggest the development of an effective strategy for immunization with pneumococcal vaccine, and provide a better understanding of possible environmental effects on conjugate immunogenicity.